An example of background art is shown in FIG. 1, which shows a laser writer for printed circuit boards, implemented as Micronic Mydata's LDI 5s system. The technology is described in several patent applications filed by the same assignee.
The figure shows the main blocks of the writer, namely a stationary part 100 containing laser source and optics, a rotor 102 which relays the laser light 114, 116 to the workpiece 106 and scans the workpiece at a relatively high speed, and finally a stage 104 holding the workpiece 106 and moving the workpiece relative to the axis of the rotor 102. The stationary part 100 contains a light source 108 which can in the general case be a laser or another light source, e.g. a collection of LEDs or an arc lamp. The light source also has optics for conditioning the light to illuminate the modulator 110, which modulates the light to create a large number of modulated light beams. In LDI 5s, which has a linear SLM as modulator, the number of light beams is approximately 8000. With a different type of modulator the number can be higher, e.g. in the range 0.5 to 1.1 million (an XGA DMD from Texas Instruments or a 2D SLM from Micronic Mydata) or around two million (HDTV DMD from Texas Instruments) or around six million (SML from ASML-IMEC). Alternatively they can be fewer, e.g. around 2000 (GLV from Silicon Light Machines) or more numerous, e.g. approximately 8 million (4k×2k DMD for digital cinema from Texas Instruments). Other sizes exist or may be developed and multiple SLMs used simultaneously may be used. Alternatively, the light source and modulator may be implemented as an array of directly modulated laser diodes or LEDs, which creates a large number of modulated beams. The wavelength in the LDI 5s is 355 nm, but other wavelengths are possible from the IR, through the visible, and down into UV and Deep UV. The third block shown in the stationary part in FIG. 1 is a focus actuator 112, which based on measured focus data, refocuses the modulated beams on the workpiece. The light 114 is bent and transported by prisms, mirrors, and optical relays (not shown in the figure except the rotating pyramid mirror 128) first into the rotor 102, and then to the surface of the workpiece 106. The rotation of the rotor 102 traces the image around a circle 124. The beams illuminate an arced swath 120 on the workpiece. Since there are several arms with optics 118, 126 and the pyramid mirror 128 always directs the light to the arm, which is positioned at, or close to the workpiece a series of arcs 122 are exposed. The stage 104 is moving slowly as the arrow 105 shows and the multiple arcs form a contiguous exposed area 123 on the workpiece 106. The exposed area is patterned by the modulated beams and a data channel (not shown) turns the beams on and off in accordance with the input data describing the pattern to be written.